Spring Cylinder Rotary Actuator

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Brendan Richards
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1 Spring Cylinder Rotary Actuator Rotary Actuator

2 Spring Cylinder Rotary Actuators High torque and pneumatic stiffness combine together in the Mascot "Spring cylinder rotary actuator" These characteristics are designed into a lightweight, rugged and compact assembly, making the Mascot rotary actuator the first choice for quarter turn applications. The Mascot rotary actuator is created for operating the DC Series high performance butterfly valve, the VB Series or other applications requiring precision in rotary motion. For throttling applications, Mascot pneumatic and electro-pneumatic positioners are available. The actuator, Mascot positioner, and cylinder uses a rocking piston for direct conversion of linear motion to rotary motion. The rocking piston assembly along with a splined shaft and lever eliminates any lost motion. (*See Tables I and II for limitations on certain sizes.) Figure 1: Spring cylinder rotary actuators Compact, lightweight design for easy handling, limited space High interchangeability reduces spare part requirements Actuator spring for fail-safe operation Rocking piston provides direct connection to shaft Sliding seal assembly for reliable long life operation Splined lever/shaft for zero lost motion Adjustable stroke stops prevent excessive rotation and reduce excessive torque on shaft 2

3 Features and Advantages Salient features and advantages of the Mascot rotary Spring cylinder actuator are : Salient features Upto 150 psi air supply Rocking piston Spined shaft and lever Rugged, Compact and Light weight Low friction bearings Field Reversible Fail-safe spring Air-purged, fully enclosed transfer case Advantages Higher torques achieved Stiff piston positioning Higher p limits on valve possible Direct connection to shaft Zero loss motion between actuator and valve Fewer parts involved Zero lost motion possible Installs in limited space applications Easy maintenance Meets seismic requirements Provide millions of cycles with minimal wear Combined with direct linkage, provides very low hysteresis No extra parts needed Fast easy field reversing possible No change of spring action needed Without pressure assistance, moves the actuator to failure position Safe operation Four monitoring positions without reducing, changing or adding parts External position indicator present Prevents corrosion of linkage Stroke stops Allow both ends of stroke to be adjusted Mascot rotary spring cylinder actuator - Capitalising on established features of other Mascot actuators: Dynamic, Interchangeability Spool-type four-way Positioner Conveniently uses indentical parts in differing rotary actuator sizes Uses many Mascot linear actuator parts Minimizes stocking of spares Minimal inventory costs Ease of calibration and maintenance due to fewer parts High performance modulating positioner control Mascot's rotary spring cylinder actuator features high torques,positioning stiffness and easy maintenance to produce a high-performance rotary actuator that excels in maintenance-free throttling and on/off control applications. 3

4 Stiffness A 25 square inch cylinder actuator (typical for a 2" valve) with a supply air pressure of 100 psi, the spring rate would be nearly 10,000 pounds per inch near the seat. As the volume under the piston becomes smaller, the stiffness factor becomes larger in a Mascot spring cylinder rotary actuator. The resulting higher actuator stiffness in cylinder actuators is that without position fluctuations caused by flow fluctuations, rotary valves can be operated in the flow-to-close orientation. Spring rate for a diaphragm actuator remains the same, irrespective of diaphragm position. An equivalent diaphragm actuator (46 square-inches) on the same valve with a 3-15 psi signal has a spring rate of less than 1000 pound per inch. Sudden changes in dynamic force can cause valve to slam shut when a rotary valve with a diaphragm actuator is operated near its closed position. As opposed to this, the stiffness of Mascot spring cylinder rotary actuators increases as the closing member approaches the sitting surface. Mascot rotary actuators and rotary valves are well operated with the valve shaft downstream or upstream. Please see Mascot's Sizing & Selection Manual, Section 16, Rotary Actuator Sizing, for more information. Figure 2: Actuator at Mid-stroke Control valves are mostly used by the process control industry for regulating constantly fluctuating flows. As the dynamic forces of a flow increase or decrease, it is mandatory to have a control valve that remains in the same position as dictated by the controller. Thus making the valve is dependent upon the actuator stiffness for minimizing these position fluctuations. Actuator stiffness can be defined as the ability of the actuator to withstand suddenly changing dynamic fluid forces acting on the valve trim. Since supply air pressure is delivered to both sides of the piston in the cylinder, the stiffness of the Mascot spring cylinder rotary actuator is significantly greater than that of a diaphragm actuator. The stiffness (spring rate) is equal to the expression: Figure 3: Actuator with High Stiffness/Spring Rate K = kpa2 v Where: K = spring rate k = ratio of specific heat P = supply pressure A 2 = piston area (in 2 ) v = cylinder volume under piston 4

Performance Torque Producing Capability Substantially high torque is produced by Mascot spring cylinder rotary actuators than the diaphragm actuators as the cylinder operates with supply pressures

Higher actuator air supply, coupled with high-pressure air on both sides of the actuator piston, provide exceptional stiffness for precise throttling control.

5 Performance Torque Producing Capability Substantially high torque is produced by Mascot spring cylinder rotary actuators than the diaphragm actuators as the cylinder operates with supply pressures upto 150 psi psi is the limit for throttling diaphragm actuators, thus decreasing their torque producing capabilities to produce higher torque. Higher actuator air supply, coupled with high-pressure air on both sides of the actuator piston, provide exceptional stiffness for precise throttling control. To permit the valve to throttle near the seal and to control high pressure drops, the stiffness of Mascot rotary actuator is sufficient. Cam Characterizable Operation Mascot's standard Valve positioner, is provided with a reversible cam that characterizes Butterfly (DiskFlo) control valve Cv to either modified equal percent or linear performance. The same cam enhances the V-Notch ball valve's inherent equal percent characteristic. A second rotary cam is also available. This optional cam gives V-Notch ball valves a linear relationship of rotation with respect to the controller signal. It is reversible for use in air-to-open, air-to-close or fail/open applications. Speed and Sensitivity Fast stroking speeds are produced with the combination of High air-handling capacity of the positioner, with relatively low cylinder volumes. High operating speed is achieved with virtually no overshoot when approaching the final disc or ball position. At the same time, static sensitivity of the unit is excellent. For example, as little as psi is required to rotate the shaft 0.01 degrees (the minimum detectable movement in the tests conducted) on a size 25 actuator. To reverse the shaft motion, a signal change of only 0.02 psi is required. Frequency Response The Mascot cylinder rotary actuator frequency response is extremely high - generally an order of magnitude better than comparable diaphragm actuator units. Such response is achieved through a double-acting configuration that uses pressure on both sides of the piston. Degrees Size 25 Actuator, 9 psi ±2 psi Relative Response db Phase Angle Frequency Hertz Figure 4: Frequency Response Hysteresis and Repeatability Any actuator should have ability to respond to signal changes from the controller and to give uniform response unaffected by decreasing or increasing pressures. Tests prove that on a full scale, hysteresis and repeatability of the spring cylinder rotary actuator, with valve positioner are less than 0.7 percent. (See Table VII: Valve Positioner Performance on page 10.) Size 25 Actuator, Signal 4.2 to 13.8 psig 13.8 psig Signal Input Signal Valve Position 4.2 psig Time (seconds) Figure 5: Step Test 5

6 Output torque Table I: Net Torque Output of Actuators at Various Supply Pressures, (in.-lb.) Actuator Supply Degrees from Fail Position on Air Supply Loss Size Pressure STD 25 with STD Spring Spring Torque STD 25 with HD Spring Spring Torque STD 50 with STD Spring Spring Torque STD 50 with HD Spring Spring Torque STD 100 with STD Spring Spring Torque STD 100 with Dual Springs Spring Torque STD 200 with 80* STD Spring Spring Torque STD 200 with 80* Dual Springs Spring Torque NOTE: For air-to-open/fail-closed actuators the 0 degree position shown above corresponds to the disc or ball being seated. For air-to-close/ fail-open actuators the 90 degree position shown above corresponds to the disc or ball being seated. * Size 200 actuator limited to 80 psi air supply - pressure 6

7 Specifications Table II: Rotary Actuator Data *Actuator Max Upper Lower Actuator Stroke Moment Air Spring Spring Cylinder Cylinder Shipping Size (inches) Arm Supply Design Rate Area Area Weight** (sq.in.) (inches) (psi) (lb./in.) (sq.in.) (sq.in.) STD 180 HD (Cap) STD 164 HD (Cap) STD 300 DUAL STD 300 DUAL * Valve in closed position ** Estimated, including Valve Positioner Table III: Actuator Specifications Type Cylinder with positive spring action Sizes 25, 50, 100 and 200 sq. in. Spring Single (std.), heavy-duty, Designs dual Action Field reversible: Air-to-open, Air-to-close Operating pressure Up to 150 psi** Temperature range -40 O F to 350 O F* * Ambient temperatures greater than 180 O F require Viton O-rings. Ambient temperatures below -40 O F require fluorosilicone O- rings. ** See Table II for limitations on certain actuators. Table IV: Stroking Speeds with Positioner* Time in Seconds Actuator Actuator for 90 O Rotation Stroke Size 1 /4" Tubing 3 /8" Tubing (inches) (standard) (optional) 25 (std) (std) (std) * Valve positioner stroking valve to fail position. Consult factory for speeds faster than those shown above. Table V: Materials of Construction Yoke Transfer case Splined lever arm Stem Bearings Sliding seal Retaining ring Piston Cylinder O-ring Actuator spring Spring button Ordering Information Ductile iron Anodized aluminum Ductile iron 416 stainless steel Filament wound fiberglass with Teflon liner Delrin 100, aluminum Cadmium plated steel Anodized aluminum Anodized aluminum Buna N (std.) Coated steel (rust proof) Painted steel or cadmium plated When ordering individual rotary actuators, the following information must be provided: 1. Operating conditions, throttling or on/off. 2. Maximum air supply pressure. 3. Valve rotation in degrees. 4. Actuator torque required at both ends of rotation. 5. Positioner and input signal range, if needed. 6. Stroking time requirements, if critical. 7

Valve Positioners Easy calibration Corrosion-resistant cover and base Withstands 150 psi at all parts Two -sided cam for easy field reversibility Optional / NPT for piped exhaust Split ranges can be

A pneumatic module for air control signals, or an electro-pneumatic (I/P) module for milliamp electrical control signals is offered with Mascot valve positioner.

These positioners being compact, field reversible, are designed for high performance and are reliable because of the rugged built.

cover and base assembly and continuously purged from the inside with instrument air making corrosion resistant internal section.

Shock and Vibration Resistant the make and design of valve positioners is such that they have high natural frequency coupled with pneumatic damping.

For Single or Double-acting Actuators The valve positioner is versatile usable with either single or double acting actuators. Standard Mounting Valve positioners use the standard mounting.

8 Valve Positioners Easy calibration Corrosion-resistant cover and base Withstands 150 psi at all parts Two -sided cam for easy field reversibility Optional / NPT for piped exhaust Split ranges can be easily adjusted Electro-pneumatic (I/P) module Pneumatic module Interchangable Figure 6: Valve Positioners Features Valve positioners are primarily utilized by Mascot. A pneumatic module for air control signals, or an electro-pneumatic (I/P) module for milliamp electrical control signals is offered with Mascot valve positioner. Valve positioners are single or double-acting, force-balanced instruments that provide fast, sensitive and accurate positioning of cylinder and diaphragm actuators. These positioners being compact, field reversible, are designed for high performance and are reliable because of the rugged built. Features P/P or I/P Signal Convertible Easy accomplishment of field conversion from one control signal to another by replacing one module with another Corrosion Resistant Epoxy powder painted on cover and base assembly and continuously purged from the inside with instrument air making corrosion resistant internal section. Internal working parts are constructed from 300 series stainless steel, anodized aluminum or Buna-N. Shock and Vibration Resistant the make and design of valve positioners is such that they have high natural frequency coupled with pneumatic damping. It is unaffected by vibration, acceleration up to 2 G s, and frequencies to 500 Hz. For Single or Double-acting Actuators The valve positioner is versatile usable with either single or double acting actuators. Standard Mounting Valve positioners use the standard mounting. By changing the cams and follower arms, the same positioner can be used on both linear and rotary actuators. This results in fewer required spare parts. 8 Easily Field Reversed A reversal of action in the field is achieved by simply turning the cam over, reversing the anti-backlash spring and changing the output tubing. Insensitive to Mounting Position Positioners can be mounted in any orientation. Simple Calibration Easy calibration as there is minimal interaction between zero and span. For protection and to discourage tampering, positioner adjustments are totally enclosed. Split-Range Service Standard signal ranges are 4-20 ma for the electro-pneumatic (I/P) module and 3-15 psi (0-1 Bar) for the pneumatic (P/P) model. Optional ranges are ma and 6-30 psi ( Bar), respectively. All models can be calibrated for a 2 or 3- way split range. Simplified Maintenance Ease in maintenance because of positioners simplicity, modular design and a few parts. Regulator not needed Designed to withstand 150 psi (10.3 bar) at all parts, the valve positioners are insensitive to supply pressure fluctuations. Low Air Consumption Steady state air consumption is psi (4.1 Bar) supply. Changeable Flow Characteristics Easily changed cam provides characterized flow feedback. High Air Flow Gain Model Standard on 200 square inch actuators and above, optional on others. Output Gauge Helps Monitor Unit: Permits easy verification of transducer and positioner calibration as it indicates transducer output to the positioner.

9 Valve Positioner Operation Figure 4 shows a valve positioner. The valve positioner is a force-balanced instrument, with pneumatic module installed on a double-acting actuator for air to open action. Positioning is based on a balance of two forces; one proportional to the instrument signal and the other proportional to the stem position. A downward force is activated as the signal pressure acts upon the diaphragms in the instrument signal capsule, through the follower arm and cam, the motion of the actuator stem is transmitted to the top end of the feedback spring resulting in the varying of tension in feedback spring as stem position changes. The system will be in equilibrium and stem will be in the position called for by the instrument signal when these opposing forces balance exactly. The balance will move up or down and by means of the spool valve, will change the output pressures and flow rate if these opposing forces are not in balance. This will lead to the piston to moving until the tension on the feedback spring opposes exactly the instrument signal pressure. The detailed sequence of positioner operations are as follows: An increase in the instrument signal forces the instrument signal capsule and balance beam downward. This motion of the balance beam also pulls the pilot valve spool downward from its equilibrium position. This opens the pilot valve ports, supplying air to port 1 and exhausting air from port 2. This causes the actuator piston upward. Proportionally to the valve position, to counter the force generated by the instrument signal capsule, the piston continues to stroke upwards until force in the feedback spring increases sufficiently. At this point the balance beam and spool begin to return to equilibrium position. As the valve spool ports start to close, the air flow rate to the actuator is decreased. The feedback spring tension force will equal the force generated in the instrument signal capsule after the piston has reached the required position. The balance beam and instrument signal capsule will remain in their equilibrium positions with no air flowing to the actuator until a change in the instrument signal is made. A proportional downward movement of the actuator piston and stem is affected by a decrease in the instrument signal which reverses the described actions. Figure 4 : Positioner Schematic for Air-to-Open (Retract) Output 2 Cylinder Piston Output 1 Range Adjustment Screw Range Adjustment Lock Screw Zero Adjustment Zero Adjustment Lock Knob Feedback Spring C Follower Arm Actuator Lever Arm Signal Balance Beam 3-15 psi Instrument Signal Capsule Pilot Valve Body Pilot Valve Spool 9

10 Specifications Table VI: Valve Positioner Specifications Specification Pneumatic Module I/P Module Input signal range: 3-15 psi, 2 or 3-way split range; 6-30 psi, 2 or 3-way split range; 4-way split range 4-20 and ma with 2 or 3 and 4-way split range Supply pressure 30 psi to 150 psi Same Ambient Standard model: -20 F to +185 F Standard model: -20 F to +180 F temperature limits Ext. temp. model: -50 F to +250 F Ext. temp. model: -40 F to +180 F Connections Supply, instrument and output: 1 /4-inch Signal: 1 /2-inch NPT elect. conduit; NPT; Gauges: 1 /8-inch NPT Output: 1 /4-inch NPT; Gauges: 1 /8-inch NPT Standard materials Stainless steel, anodized aluminum, Same nickel-plated steel, epoxy powderpainted steel and Buna-N Loop Load N/A 5.3 volts + 5 ohms (270 ohms at 20 ma) Hazardous Location Approvals (FM and CSA approved) N/A Intrinsically safe: Class I, Division 1, Groups A, B, C, D; Class II, Groups E, F, G Explosion-proof: Class I, Division 1, Groups B, C, D; Class II, Groups E, F, G Non-incendive: Class I, Division 2, Groups A, B, C, D, F, G Net weight 3 lbs. 5.5 lbs. Table VII: Valve Positioner Performance* Pneumatic IP 2000 Module Module Independent Linearity - Maximum deviation from a best fit straight line +1.0% F.S. +1.0% F.S. Hysteresis - Maximum position error for the same value of input when 0.5% F.S. 0.5% F.S. approached from opposite ends of the scale. Repeatability - Maximum variation in position for the same value of input when 0.2% F.S. 0.2% F.S. approached from the same direction. Response Level- Maximum change in input required to cause a change in 0.2% F.S. 0.2% F.S. valve stem position in one direction. Dead Band - Maximum change in input required to cause a reversal in valve 0.3% F.S. 0.3% F.S. stem movement. Resolution - Smallest possible change in valve stem position..1% F.S..1% F.S. Steady State Air 60 psi.25 SCFM.31 SCFM Supply Pressure Effect - Position change for a 10 psi supply pressure change..05 % F.S..06% F.S. "Open-loop" Gain - Ratio of cylinder pressure unbalance to instrument 300:1 psi/psi 400:1 psi/ma pressure change with locked psi Maximum Flow 60 psi 11 SCFM 11 SCFM Frequency Response - -6 db Frequency.8 Hz.8 Hz (With sinusoidal input of ±5% F.S. centered about 50% F.S.) Phase Angle at -6dB -71 O O Stroking Speed - Closed to open in/sec. 2.3 in/sec. Open to closed in/sec. 1.3 in./sec. *Data is based on tests of the Valve positioner mounted on a double-acting cylinder actuator having a piston area of 25 square inches with a valve stroke of 1.5 inches and 60 psi supply pressure. Instrument signal was 3-15 psi with pneumatic module and 4-20 ma with I/P module. 10

Accessories Declutchable Handwheel Actuator It has been designed to override the actuator in case of air failure or if manual operation is desired.

Position indicator (PT Series) Position indicator is a position transmitter that exceeds the capabilities of normal limit switches by providing a continuous electrical output signal proportional to

11 Accessories Declutchable Handwheel Actuator It has been designed to override the actuator in case of air failure or if manual operation is desired. A special high-output worm gear develops as much torque as the standard Mascot pneumatic rotary actuator. Position indicator (PT Series) Position indicator is a position transmitter that exceeds the capabilities of normal limit switches by providing a continuous electrical output signal proportional to the position of the control valve. Position indicator operates with two wires on a 4 to 20 ma DC voltage, ensuring infinite resolution for safe, dependable monitoring of a control valves position to within linearity ± 1 percent. Mounted on the transfer case opposite the valve, the infinite resolution potentiometer is easily adjusted with zero and span settings for field calibration. Position indicator models may contain a potentiometer and transmitter, two or four limit switches, or a combination of a transmitter and two limit switches. (Weather and explosion-proof protection from external conditions is provided A rugged. Sudden changes) Manual Handwheel Actuator (Applications requiring infrequent use but reliable operation, a high-torque, manual handwheel actuator is available.) There are three sizes to match the torque requirements of any application. For maintenance free operation, the sealed housing is made of cast iron and filled with grease. Heavy-duty Springs For high shutoff pressure, heavy-duty springs are available. A spring cap installed in the cylinder is used for high pressure drop applications, requiring the installation of the longer heavy-duty spring. The same spring can be used for both fail-open and fail-closed applications. Dual springs are available with 100 and 200 square-inch rotary actuators. Solenoid Valves To interrupt the instrument signal to the pneumatic positioner, the three-way solenoid valve is used. For on/off applications where throttling is not required, only four-way solenoid valve (without the Positioner ) is used. It ensures fast, positive, two-directional action. Solenoid valves are available in both AC and DC voltages. Air Filters An air filter is recommended for installation upstream of the positioner. It features high flow capacity and handles up to 150 psi supply air pressure. Easy access to the large drip well permits inspection and replacement of the filter cartridge, while the integral drain valve allows removal of trapped oil, moisture and other foreign material. Regulators are usually not required with Mascot actuators and positioners. 11

12 Dimensions J E DISASSEMBLY CLEARENCE F H O S S G S K C FF R SHUT OPEN P M O S S N Table VIII: Rotary Actuator Dimensions (inches/mm) Size C* E F FF G H J K M N P R S** Press. (in.) (act) Conn /4 NPT /4 NPT N/A N/A /4 NPT N/A N/A /4 NPT *7.8/198 on size 100 and 200 actuators, 16-inch and larger valves. **7.9/202 on size 50 actuators and 8, 10-inch valves; 9.4/238 on size 100, 200 actuators and 8,10,12-inch valves; 11.3/286 on size 100, 200 actuators and 16-inch and larger valves. NOTE: Size 100 and 200 actuators do not include lifting rings.

Control Valves Positioner

Control Valves Positioner HiFlo Valve Positioner Easy calibration Corrosion-resistant cover and base Withstands 150 psi at all parts Two -sided cam for easy field reversibility Optional / NPT for piped